Effect of a blend-grind-peen repair technique on subsequent fatigue behaviour of a low-pressure shot peened steam turbine blade material

In this study, a blend-grind-peen repair technique was applied to a 12-Cr tempered martensitic steam turbine blade material containing a pre-existing fatigue crack. Manually grinding out the crack increased the elastic stress concentration factor K t from 1.6 to 1.8. The repaired sample which was not re-peened showed a ∼50% improvement in cycles to failure compared with baseline samples. Sub-surface coalescence effects in shot peened surfaces are not always evident from surface crack measurements, which has implications for considering how much material to remove in such a repair. Despite the presence of a pre-existing crack, re-peening slowed the growth of the crack and extended the lifetime beyond that expected in the original shot peened surface.